Hydrostatic pump or motor with spherical piston

ABSTRACT

A hydraulic energy converting device applicable to both pumps and motors, such devices employing an obliquely pivoted swash plate to interact with a spherical piston. The axial component of the force on the piston causes wear. This wear is minimized by providing a bowl-shaped piston with a ball-contacting seat and interposing a ball between the piston and the swash plate. Pressure-communicating arrangements in the piston permit fluid pressure and the ball to interact directly, minimizing the force of contact between ball and seat.

United States Patent inventor Per Fryklund Vasteras, Sweden Appl. No. 842.522 Filed July 17, 1969 Patented July 13, 1971 Assignee Allmauna Svenska Elektriska Aktiebolaget Vasteras, Sweden Priority July 23, 1968 Sweden HYDROSTATIC PUMP OR MOTOR WITH SPHERTCAL PISTON 3 Claims, 2 Drawing Figs.

U.S. Cl 92/54, 92/172, 92/181 Int. Cl ..F0lb- 13/00, F16 1/24 Field of Search 92/ l 72, 181,178,179, 5.4.56-58; l03/l36 A, 161 B; 91/123 References Cited UNITED STATES PATENTS 459,735 9/1891 Benham ..l.03/161X(BALL) 1,325,434 12/1919 Carey etal 103/161 (BALL) 2,712,794 7/1955 Humphreys... .....1D3/l61 (BALL) 3,056,357 10/1962 Bohnhoff ..l03/161 (BALL) 3,264,951 8/1966 Dobrikin 92/64 3,366,017 1/1968 Firth etal. 92/131 X 3,435,774 4/1969 Parrett 92/181 X 3,435,775 4/1969 Parrett 103/162 Primary ExaminerMartin P. Schwadron Assistant Examiner-Irwin C. Cohen Attorney-Jennings Bailey, Jr.

ABSTRACT: A hydraulic energy converting device applicable to both pumps and motors, such devices employing an obliquely pivoted swash plate to interact with a spherical piston. The axial component of the force on the piston causes wear. This wear is minimized by providing a bowl-shaped piston with a ball-contacting seat and interposing a ball between the piston and the swash plate. Pressure-communicating arrangements in the piston permit fluid pressure and the ball to interact directly, minimizing the force of contact between ball and seat.

PATENTEUJuu 31911 3592105 INVEN PE R FRYK I.

HYDROSTATIC PUMP R MOTOR WITH SPHERICAL PISTON The present invention relates to an hydraulic energy converting device, that is, a pump or motor having at least one operating cylinder with an axially reciprocating, slidably mounted spherical piston driven by a cam disc a so-called swash plate or by a disc which is mounted obliquely in relation to the cylinder. There are usually several cylinders in such a pump or motor unit. The cylinders may either be parallel with or perpendicular to the axis of rotation of the pump. The cam disc may be situated either inside or outside the pump housing with the operating cylinders.

Small hydraulic pumps or motors with a ball as piston can be manufactured extremely cheaply but those manufactured so far have in many cases been inefficient. Since the ball piston interacts with a cam disc or the like and is thereby subjected to a radial force, the ball is worn and also one side of the cylinder. In pumps or motors having ball pistons there is a line contact between the bore and the piston, which means that the efficiency decreases rapidly as the gap between the bore and the piston increases.

According to the invention a pump or motor is obtained having most of the advantages of the ball motors heretofore shown in the form of simplicity and cheapness, but without all of their disadvantages. According to the invention a spherical piston is constructed with a seat for a ball running in the same cylinder as the piston, through which the camming means such as a driving force is transmitted between the driving disc or swash plate and the piston. The seat is spherically annular and the piston bowl shaped so that a space is formed between the ball and the piston inside the contact surface. This space is in communication with the space in front of the piston by means of a channel in the piston so that a considerable part of the force of interaction between ball and cam disc is balanced by the pressure medium.

The invention is further described with reference to the accompanying drawings. FIG. I shows a cylinder with piston and ball in perfect condition and FIG. 2 the same cylinder when the ball and cylinder have become considerably worn.

In the drawings, 1 designates a part of a pump or motor housing, not otherwise shown, having an operating cylinder 2 in which run a spherical piston 3 and a ball 4 which interacts with a swash plate 5 which, when it pivots, drives or is driven by the piston 3 via the ball 4. The piston 3 is bowl shaped and has an annular seat 6 so that a space 7 is formed inside the seat between the piston and the ball, the space 7 communicating through a channel 8 with the space 9 in the cylinder 2 in front of the piston 3. The space 9 is in communication through valves, not shown, in the channel 10 with a container and, for example a pressure accumulator. The piston is shown in its outmost position, but its innermost position is indicated in the drawings by the dotted line 11. In FIG. 2 the ball has worn a groove 12 in the wall subjected to lateral pressure from the ball. A gap 13 has thus been formed between the ball and the cylinder wall, which is widest opposite the groove 12. In the pump or motor shown the piston 3 is not subjected to any lateral force so that its wear is negligible. Because the piston is spherical an inclination such as that in FIG. 2 is of no importance. The pressure medium influences piston and ball with force symbolized by arrows. Thanks to the connection between the spaces 7 and 9 a considerable part of the force is transferred between the ball and the piston through the pressure medium enclosed in the space 7. The contact pressure between the ball and the seat 6 can thus be kept so low that the ball can easily rotate in the seat so that it becomes evenly worn and does not cut when it rotates. By a suitable design of the bowl shaped space in the piston 3 the wall between the seat 6 and the front surface of the piston can be given such a thickness that the rear part of the piston, because of the pressure in the space 7, expands depending on the pressure in the cylinder so that the clearance between piston and cylinder wall decreases at increasing pressure. An improved seal and thus improved eff ciency is thus obtained.

The invention IS of course not limited to the embodiment shown in the drawings. Many variations are feasible within the scope of the following claims. For instance, the wall immediately below the ball may be'made slightly conical with a cone angle determined by the greatest inclination likely to occur. The diameter of the seat can thus be increased and most of the load between ball and piston can thus be hydraulically balanced.

Iclaim:

1. In an hydraulic energy converting device having at least one operating cylinder with a piston reciprocable therein and having a spherical surface engaging the cylinder wall, camming means, a ball between said piston and said camming means for transmitting driving forces between said camming means and said piston, the improvement wherein said spherical piston contains a concave seat for said force-transmitting ball.

2. The improvement of claim 1 wherein said concave seat includes an annular, spherical contact surface, whereby a space is defined between said ball seated on said contact surface and said piston.

3. The improvement of claim 2 further comprising means in said piston to provide pressure communication between said space and the space in front of the piston. 

1. In an hydraulic energy converting device having at least one operating cylinder with a piston reciprocable therein and having a spherical surface engaging the cylinder wall, camming means, a ball between said piston and said camming means for transmitting driving forces between said camming means and said piston, the improvement wherein said spherical piston contains a concave seat for said force-transmitting ball.
 2. The improvement of claim 1 wherein said concave seat includes an annular, spherical contact surface, whereby a space is defined between said ball seated on said contact surface and said piston.
 3. The improvement of claim 2 further comprising means in said piston to provide pressure communication between said space and the space in front of the piston. 